Prop

ABSTRACT

A prop which includes first and second telescopically engaged tubular members, wherein at least one member is internally pressurized with water and wherein yielding is controlled by means of a friction ring acting between opposing surfaces of the two members and by a release valve which controls the pressure of the water.

BACKGROUND OF THE INVENTION

This invention relates to a prop suitable for use, for example, in anunderground excavation in order to provide support between a footwalland an opposed hanging wall.

The specification of South African patent No. 95/6530 describes a propof the aforementioned kind which includes two interengaged,telescopically movable, tubular members. A mouth of one member isflared. The other member enters the flared mouth and a conical frictionring is positioned in the flared mouth engaged with opposing surfaces ofthe tubular members. This prop can be prestressed by using hydraulicpressure which forces the tubular members telescopically apart. Yieldingof the prop takes place, as one member moves into the other member, withthe friction ring providing a restraining force against this telescopicmovement.

Through suitable design and with the correct choice of materials a propof the aforementioned kind can be constructed to withstand a substantialforce e.g. of the order of 65 tons, before yielding commences. However,certain mining applications call for the capability of a prop to beloaded to a higher level, e.g. of the order of 100 tons, before yieldingtakes place. This figure is not readily attainable, though, when theconical friction ring is used as a restraining and, ultimately, as ayielding, member.

An object of the present invention is to provide a prop which attemptsto address the aforementioned requirement.

SUMMARY OF THE INVENTION

The invention provides a prop which includes a first tubular member witha closed first end and a flared mouth at an opposed, second end, asecond tubular member which extends into the first tubular member,through the flared mouth, which has one end inside the first tubularmember and an opposed end which is sealed, a one-way filler valveconnected to one of the tubular members through which a pressurisedfluid can be introduced, at least, into an interior of the first tubularmember, a seal which acts between the tubular members and which permitsoutward telescopic movement of the second tubular member relative to thefirst tubular member as an interior of, at least, the first tubularmember is pressurised, a component which is located in the flared moutharound the second tubular member and which is frictionally engaged with,at least, an outer surface of the second tubular member, and a pressurerelief valve which allows fluid to escape at least from an interior ofthe first tubular member, when the pressure of the fluid reaches apredetermined value, as the second tubular member is telescopicallymoved into the first tubular member.

The pressurized fluid may also be introduced into an interior of thesecond tubular member.

The seal may act between an outer surface of a part of the secondtubular member which is positioned inside the first tubular member, andan opposing surface of the first tubular member.

Depending on the nature of the seal, fluid under pressure may bepermitted to escape from an interior of the first tubular member into aninterior of the second tubular member. Alternatively, fluid may escapefrom the first tubular member into atmosphere, or from the first and thesecond tubular members into atmosphere.

BRIEF DESCRIPTION OF THE DRAWING

The invention is further described by way of example with reference tothe accompanying drawing which illustrates from one side and incross-section a prop according to the invention in an installedconfiguration.

DESCRIPTION OF PREFERRED EMBODIMENT

The accompanying drawing illustrates a prop 10 according to theinvention installed in an underground excavation 12 and positionedbetween a footwall 14 and a hanging wall 16.

The prop includes a first elongate tubular member 20 with a lower end 22which is sealed by means of a domed closure 24. An opposing second end26 of the first tubular member has an open mouth 28 formed by a flaredsection 30 of the member.

A second tubular member 34 is telescopically engageable with the firsttubular member. The second member has a slightly smaller diameter thanthe first member to allow this type of interengagement. An upper end ofthe second tubular member is sealed by means of a domed closure 36. Alower opposed end 38 of the second tubular member is, in one embodimentof the invention, closed and carries a seal 40 which is in intimatesealing contact with an inner surface 42 of the first tubular member.

A conically shaped friction ring 44 is positioned inside the flaredmouth 28 surrounding an opposing surface of the second tubular member.The ring carries formations, not shown, at least on its inner surface 46which help the ring to engage frictionally with an outer surface 50 ofthe second tubular member.

A one-way filler valve 54 is attached at a suitable location to thefirst tubular member. Pressurised fluid, e.g. water, derived from asuitable source, not shown, is passed through the filler valve 54 usinga suitable connection and an interior 56 of the second tubular member,up to the seal 40, can thereby be filled with water and can bepressurised.

With the prop in the orientation shown in the attached drawing, as thevolume 56 is pressurised the tubular members are telescopicallyextended, moving, respectively, towards the footwall 14 and the hangingwall 16. In this way the prop is placed under a predeterminedcompressive load. Subsequently the friction ring 44 is hammered using asuitable tool, not shown, deeper into the conical mouth to ensure thatit is firmly wedged in position and is frictionally engaged with theouter surface 50 of the second tubular member.

Normally, water is then allowed to flow freely from the volume 56 and,when yielding of the prop takes place, the yielding action is controlledby movement of the second tubular member into the first tubular memberwith the friction ring 44 tending to restrain such movement.

In accordance with one form of the present invention the pressurisedfluid (water) is retained inside the volume 56. A pressure relief valve60 is attached to the first tubular member. This valve will only openand allow water to flow from the volume 56 to atmosphere when thepressure of the water is in excess of a predetermined minimum. In otherwords the pressurised water restrains the prop from yielding until thewater pressure exceeds a pre-set maximum value. At this point yieldingis controlled by the combined actions of the pressure relief valve 60and of the friction ring 44.

In a second form of the invention the pressure relief valve 60 isdispensed with and is replaced by a pressure relief valve 62 fixed tothe closed end 38 of the second tubular member. The yielding action is,however, similar to what has been described but, in this event, onceyielding commences, pressurised water is displaced from the volume 56through the valve 62 into an interior 66 of the second tubular member.

In a third, preferred, variation of the invention neither of the valves60 and 62 is used. Instead a pressure relief valve 64 is attached to awall of the second tubular member. Additionally, an interior 66 of thesecond tubular member is filled with pressurised water at the same timeas the first tubular member is pressurised. In other words a fullinterior of the prop contains pressurised water and thereby ispressurised. For this to occur a flow passage which permits free waterflow is provided at the end 38 of the second tubular member. The seal 40would then, for example, fit between an outer surface of the secondtubular member, which is inside the first tubular member, and an opposedinner surface of the first tubular member. When the pressure of thewater reaches a value at which the valve 64 opens, water is expelled toatmosphere through the valve. Yielding is controlled by the release ofwater from the prop and by the mechanical and frictional action of thefriction ring 44 acting on the outer surface 50 of the second tubularmember.

The two tubular members, included in the prop, can be made physicallystrong enough to withstand substantial loads. The prop can also beengineered, in respect of its slenderness ratio, so that it does notbuckle when subjected to a high load. A yielding characteristic which isproduced at a high load is, however, controlled by the combined actionof the release of the pressurised water from inside the prop via thepressure relief valve 64 and by the mechanical/friction action of thering 44.

1. A prop which includes a first tubular member with a closed first endand a flared mouth at an opposed, second end, a second tubular memberwhich extends into the first tubular member, through the flared mouth,which has one end inside the first tubular member and an opposed endwhich is sealed, a one-way filler valve connected to one of the tubularmembers through which a pressurised fluid can be introduced, at least,into an interior of the first tubular member, a seal which acts betweenthe tubular members and which permits outward telescopic movement of thesecond tubular member relative to the first tubular member as aninterior of, at least, the first tubular member is pressurised, acomponent which is located in the flared mouth around the second tubularmember and which is frictionally engaged with, at least, an outersurface of the second tubular member, and a pressure relief valve whichallows fluid to escape at least from an interior of the first tubularmember, when the pressure of the fluid reaches a predetermined value, asthe second tubular member is telescopically moved into the first tubularmember.
 2. A prop according to claim 1 wherein the pressurized fluid isalso introduced into an interior of the second tubular member.
 3. A propaccording to claim 1 wherein the seal acts between an outer surface of apart of the second tubular member which is positioned inside the firsttubular member, and an opposing surface of the first tubular member. 4.A prop according to claim 1, wherein fluid under pressure is permittedto escape from an interior of the first tubular member into an interiorof the second tubular member.
 5. A prop according to claim 1, whereinfluid under pressure is permitted to escape from the first tubularmember into atmosphere.
 6. A prop according to claim 1, wherein fluidunder pressure is permitted to escape from the first and the secondtubular members into atmosphere.